1. Field of Invention
The present invention relates to a method for producing hydrogen gas. More particularly, the present invention relates to a method of hydrogen gas production from reforming of methanol at low temperatures.
2. Description of Related Art
The fuel cell is a prosperous technology in progress. It can efficiently transform chemical energy in fuel into electricity in an environment-friendly manner. Amongst fuel cells under development, hydrogen fuel cell is preeminent because it can be operated at a low temperature of 200° C. or less. However, hydrogen is inconvenient to store and transport. These shortcomings can be technically overcome by using hydrocarbons as source outer primary fuel and transformed it into hydrogen-rich gas (HRG) on board of fuel cell application. HRG is a gas mixture with high hydrogen content and it is one of the fuels suitable for fuel cells.
Production of HRG from reforming of methanol has been widely studied because it is highly chemically active, abundant, and cheap. Many methanol reforming processes have been developed in literature. Early methods are “steam reforming of methanol” (SRM) and “partial oxidation of methanol” (POM):CH3OH+H2O→3H2+CO2ΔH=49 kJ mol−1   (1)CH3OH+½O2→2H2+CO2ΔH=−192 kJ mol−1   (2)
Reaction SRM has a high hydrogen yield (number of hydrogen molecule produced from each consumed methanol molecule) of RH2=3.0. However, the endothermic reaction does not theoretically favor at low temperatures. According to Le Chatelier's Principle, SRM becomes efficient at high temperatures. Comparatively, exothermic POM is favored at lower temperatures and produces HRG with low CO contamination. However, a low hydrogen yield of RH2=2.0 is produced.
A more advanced process is called “oxidative steam reforming of methanol” (OSRM). OSRM uses a mixture of water vapor and oxygen as oxidant. In other words, it is a combination of reactions 1 and 2 in an optional ratio. A negligible reaction heat may occur as the ratio is 3.9/1. On one hand a desirably high RH2 (>2.0) may be generated by OSRM due to addition of steam, and on the other hand the CO content in HRG and the reaction temperature can be decreased due to the presence of oxygen.
There are many OSRM-related references. Some use supported copper catalysts such as Cu/ZnO—Al2O3 and Cu/ZrO2, as disclosed in US published application 2002/0019324, Hozle et al., U.S. Pat. No. 6,576,217, Nojima et al., and WO published application 2004/083116, Schloglet et al., for example. Some use Pd/CeO2—ZrO2 catalyst, as disclosed in US published application 2001/0021469A1 and 2001/0016188 A1, Kanekim et al., or Pd—Cu/ZnO alloy catalyst, as disclosed in WO published patent 96/00186, Edwards et al. These catalysts require a reaction temperature of TR>200° C. to catalyze OSRM and the selectivity of CO (instead of the aimed CO2) in product is high (Sco>2). CO is notorious for poisoning Pt catalyst, deactivating the catalyst and damaging the performance of the PEMFC. If copper catalyst dispersed on mixed zinc, aluminum and zirconium oxide is used, the CO selectivity may be decreased to Sco<1% (US 2005/0002858, published, Suzuki et al.), but a TR>200° C. remains required.
Table 1 shows the comparisons of different catalyst systems to the OSRM in other known references. It is observed that all of the catalyst systems require a temperature of TR>200° C. to effectively catalyze the OSRM.
TABLE 1Comparison of different catalyst system to the OSRMcatalystTRsystemxw(° C.)CMeOHRH2SCOsourcesCuZnAlZr0.251.3227952.61Velu(1)CuZnAl0.31.132572.61.82.1Fierro(2)CuZnAlZr0.31.3227802.80.7Velu(3)CuZnAl0.471.432271002.450.19Shen(4)CuZnZrCe0.251.622778.52.90.58Velu(5)CuZnAl0.1250.7527780—2.6Geissler(6)CuCoZnAl1.60.25227502.530Velu(7)Pd/ZnO0.11.524774—4Liu(8)Remarks: x stands for oxygen/methanol, and w is water/methanol.CMeOH = [n(MeOH)in − n(MeOH)out]/n(MeOH)inSCO = n(CO)out/[n(CO)out + n(CO2)out]RH2 = n(H2)out/n(MeOH)in − n(MeOH)out](1)Velu, S., Suzuki, K., and Osaki, T., Catal. Lett. 62, 159 (1999);(2)Murcia-Mascaros, S., Navarro, R. M., Gomez-Sainero L. Costantino, U., Nocchetti, M., and Fierro, J. L. G., J. Catal. 198, 338 (2001);(3)Velu, S., Suzuki, K., Kapoor, M. P., Ohashi, F., and Osaki, T., Appl. Catal. A: 213, 47 (2001);(4)Shen, J-P., and Song C., Catal. Today 77, 89 (2002);(5)Velu, S., and Suzuki, K., Topics in Catal. 22, 235 (2003);(6)Geissler, K., Newson, E., Vogel, F., Truong, T., Hottinger, P., and Wokaun, A., Phys. Chem. Chem. Phys. 3, 189 (2001);(7)Velu, S., and Suzuki, K., J. Phys. Chem. B 106, 12737 (2002);(8)Liu, S., Takahashi, K., and Ayabe, M., Catal. Today 87, 247 (2003).